GTK v1.2 Tutorial: The Button Widget

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## 6. The Button Widget

## 6.1 Normal Buttons

We've almost seen all there is to see of the button widget. It's pretty simple. There are however two ways to create a button. You can use the gtk_button_new_with_label() to create a button with a label, or use gtk_button_new() to create a blank button. It's then up to you to pack a label or pixmap into this new button. To do this, create a new box, and then pack your objects into this box using the usual gtk_box_pack_start, and then use gtk_container_add to pack the box into the button.

Here's an example of using gtk_button_new to create a button with a picture and a label in it. I've broken up the code to create a box from the rest so you can use it in your programs. There are further examples of using pixmaps later in the tutorial.

> `

>     /* example-start buttons buttons.c */

>     #include <gtk/gtk.h>

>     /* Create a new hbox with an image and a label packed into it
>      * and return the box. */

>     GtkWidget *xpm_label_box( GtkWidget *parent,
>                               gchar     *xpm_filename,
>                               gchar     *label_text )
>     {
>         GtkWidget *box1;
>         GtkWidget *label;
>         GtkWidget *pixmapwid;
>         GdkPixmap *pixmap;
>         GdkBitmap *mask;
>         GtkStyle *style;

>         /* Create box for xpm and label */
>         box1 = gtk_hbox_new (FALSE, 0);
>         gtk_container_set_border_width (GTK_CONTAINER (box1), 2);

>         /* Get the style of the button to get the
>          * background color. */
>         style = gtk_widget_get_style(parent);

>         /* Now on to the xpm stuff */
>         pixmap = gdk_pixmap_create_from_xpm (parent->window, &mask,
>                                              &style->bg[GTK_STATE_NORMAL],
>                                              xpm_filename);
>         pixmapwid = gtk_pixmap_new (pixmap, mask);

>         /* Create a label for the button */
>         label = gtk_label_new (label_text);

>         /* Pack the pixmap and label into the box */
>         gtk_box_pack_start (GTK_BOX (box1),
>                             pixmapwid, FALSE, FALSE, 3);

>         gtk_box_pack_start (GTK_BOX (box1), label, FALSE, FALSE, 3);

>         gtk_widget_show(pixmapwid);
>         gtk_widget_show(label);

>         return(box1);
>     }

>     /* Our usual callback function */
>     void callback( GtkWidget *widget,
>                    gpointer   data )
>     {
>         g_print ("Hello again - %s was pressed\n", (char *) data);
>     }

>     int main( int   argc,
>               char *argv[] )
>     {
>         /* GtkWidget is the storage type for widgets */
>         GtkWidget *window;
>         GtkWidget *button;
>         GtkWidget *box1;

>         gtk_init (&argc, &argv);

>         /* Create a new window */
>         window = gtk_window_new (GTK_WINDOW_TOPLEVEL);

>         gtk_window_set_title (GTK_WINDOW (window), "Pixmap'd Buttons!");

>         /* It's a good idea to do this for all windows. */
>         gtk_signal_connect (GTK_OBJECT (window), "destroy",
>                             GTK_SIGNAL_FUNC (gtk_exit), NULL);

>         gtk_signal_connect (GTK_OBJECT (window), "delete_event",
>                             GTK_SIGNAL_FUNC (gtk_exit), NULL);

>         /* Sets the border width of the window. */
>         gtk_container_set_border_width (GTK_CONTAINER (window), 10);
>         gtk_widget_realize(window);

>         /* Create a new button */
>         button = gtk_button_new ();

>         /* Connect the "clicked" signal of the button to our callback */
>         gtk_signal_connect (GTK_OBJECT (button), "clicked",
>                             GTK_SIGNAL_FUNC (callback), (gpointer) "cool button");

>         /* This calls our box creating function */
>         box1 = xpm_label_box(window, "info.xpm", "cool button");

>         /* Pack and show all our widgets */
>         gtk_widget_show(box1);

>         gtk_container_add (GTK_CONTAINER (button), box1);

>         gtk_widget_show(button);

>         gtk_container_add (GTK_CONTAINER (window), button);

>         gtk_widget_show (window);

>         /* Rest in gtk_main and wait for the fun to begin! */
>         gtk_main ();

>         return(0);
>     }
>     /* example-end */

> `

The xpm_label_box function could be used to pack xpm's and labels into any widget that can be a container.

Notice in `xpm_label_box` how there is a call to `gtk_widget_get_style`. Every widget has a "style", consisting of foreground and background colors for a variety of situations, font selection, and other graphics data relevant to a widget. These style values are defaulted in each widget, and are required by many GDK function calls, such as `gdk_pixmap_create_from_xpm`, which here is given the "normal" background color. The style data of widgets may be customized, using GTK's rc files.

Also notice the call to `gtk_widget_realize` after setting the window's border width. This function uses GDK to create the X windows related to the widget. The function is automatically called when you invoke `gtk_widget_show` for a widget, and so has not been shown in earlier examples. But the call to `gdk_pixmap_create_from_xpm` requires that its `window` argument refer to a real X window, so it is necessary to realize the widget before this GDK call.

The Button widget has the following signals:

- `pressed` - emitted when pointer button is pressed within Button widget
- `released` - emitted when pointer button is released within Button widget
- `clicked` - emitted when pointer button is pressed and then released within Button widget
- `enter` - emitted when pointer enters Button widget
- `leave` - emitted when pointer leaves Button widget

## 6.2 Toggle Buttons

Toggle buttons are derived from normal buttons and are very similar, except they will always be in one of two states, alternated by a click. They may be depressed, and when you click again, they will pop back up. Click again, and they will pop back down.

Toggle buttons are the basis for check buttons and radio buttons, as such, many of the calls used for toggle buttons are inherited by radio and check buttons. I will point these out when we come to them.

Creating a new toggle button:

> `

>     GtkWidget *gtk_toggle_button_new( void );

>     GtkWidget *gtk_toggle_button_new_with_label( gchar *label );

> `

As you can imagine, these work identically to the normal button widget calls. The first creates a blank toggle button, and the second, a button with a label widget already packed into it.

To retrieve the state of the toggle widget, including radio and check buttons, we use a construct as shown in our example below. This tests the state of the toggle, by accessing the `active` field of the toggle widget's structure, after first using the `GTK_TOGGLE_BUTTON` macro to cast the widget pointer into a toggle widget pointer. The signal of interest to us emitted by toggle buttons (the toggle button, check button, and radio button widgets) is the "toggled" signal. To check the state of these buttons, set up a signal handler to catch the toggled signal, and access the structure to determine its state. The callback will look something like:

> `

>     void toggle_button_callback (GtkWidget *widget, gpointer data)
>     {
>         if (GTK_TOGGLE_BUTTON (widget)->active)
>         {
>             /* If control reaches here, the toggle button is down */

>         } else {

>             /* If control reaches here, the toggle button is up */
>         }
>     }

> `

To force the state of a toggle button, and its children, the radio and check buttons, use this function:

> `

>     void gtk_toggle_button_set_active( GtkToggleButton *toggle_button,
>                                       gint             state );

> `

The above call can be used to set the state of the toggle button, and its children the radio and check buttons. Passing in your created button as the first argument, and a TRUE or FALSE for the second state argument to specify whether it should be down (depressed) or up (released). Default is up, or FALSE.

Note that when you use the gtk_toggle_button_set_active() function, and the state is actually changed, it causes the "clicked" signal to be emitted from the button.

> `

>     void gtk_toggle_button_toggled (GtkToggleButton *toggle_button);

> `

This simply toggles the button, and emits the "toggled" signal.

## 6.3 Check Buttons

Check buttons inherit many properties and functions from the the toggle buttons above, but look a little different. Rather than being buttons with text inside them, they are small squares with the text to the right of them. These are often used for toggling options on and off in applications.

The two creation functions are similar to those of the normal button.

> `

>     GtkWidget *gtk_check_button_new( void );

>     GtkWidget *gtk_check_button_new_with_label ( gchar *label );

> `

The new_with_label function creates a check button with a label beside it.

Checking the state of the check button is identical to that of the toggle button.

## 6.4 Radio Buttons

Radio buttons are similar to check buttons except they are grouped so that only one may be selected/depressed at a time. This is good for places in your application where you need to select from a short list of options.

Creating a new radio button is done with one of these calls:

> `

>     GtkWidget *gtk_radio_button_new( GSList *group );

>     GtkWidget *gtk_radio_button_new_with_label( GSList *group,
>                                                 gchar  *label );

> `

You'll notice the extra argument to these calls. They require a group to perform their duty properly. The first call to gtk_radio_button_new_with_label or gtk_radio_button_new_with_label should pass NULL as the first argument. Then create a group using:

> `

>     GSList *gtk_radio_button_group( GtkRadioButton *radio_button );

> `

The important thing to remember is that gtk_radio_button_group must be called for each new button added to the group, with the previous button passed in as an argument. The result is then passed into the next call to gtk_radio_button_new or gtk_radio_button_new_with_label. This allows a chain of buttons to be established. The example below should make this clear.

You can shorten this slightly by using the following syntax, which removes the need for a variable to hold the list of buttons. This form is used in the example to create the third button:

> `

>          button2 = gtk_radio_button_new_with_label(
>                      gtk_radio_button_group (GTK_RADIO_BUTTON (button1)),
>                      "button2");

> `

It is also a good idea to explicitly set which button should be the default depressed button with:

> `

>     void gtk_toggle_button_set_active( GtkToggleButton *toggle_button,
>                                       gint             state );

> `

This is described in the section on toggle buttons, and works in exactly the same way. Once the radio buttons are grouped together, only one of the group may be active at a time. If the user clicks on one radio button, and then on another, the first radio button will first emit a "toggled" signal (to report becoming inactive), and then the second will emit its "toggled" signal (to report becoming active).

The following example creates a radio button group with three buttons.

> `

>     /* example-start radiobuttons radiobuttons.c */

>     #include <gtk/gtk.h>
>     #include <glib.h>

>     gint close_application( GtkWidget *widget,
>                             GdkEvent  *event,
>                             gpointer   data )
>     {
>       gtk_main_quit();
>       return(FALSE);
>     }

>     int main( int   argc,
>               char *argv[] )
>     {
>         GtkWidget *window = NULL;
>         GtkWidget *box1;
>         GtkWidget *box2;
>         GtkWidget *button;
>         GtkWidget *separator;
>         GSList *group;

>         gtk_init(&argc,&argv);

>         window = gtk_window_new (GTK_WINDOW_TOPLEVEL);

>         gtk_signal_connect (GTK_OBJECT (window), "delete_event",
>                             GTK_SIGNAL_FUNC(close_application),
>                             NULL);

>         gtk_window_set_title (GTK_WINDOW (window), "radio buttons");
>         gtk_container_set_border_width (GTK_CONTAINER (window), 0);

>         box1 = gtk_vbox_new (FALSE, 0);
>         gtk_container_add (GTK_CONTAINER (window), box1);
>         gtk_widget_show (box1);

>         box2 = gtk_vbox_new (FALSE, 10);
>         gtk_container_set_border_width (GTK_CONTAINER (box2), 10);
>         gtk_box_pack_start (GTK_BOX (box1), box2, TRUE, TRUE, 0);
>         gtk_widget_show (box2);

>         button = gtk_radio_button_new_with_label (NULL, "button1");
>         gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0);
>         gtk_widget_show (button);

>         group = gtk_radio_button_group (GTK_RADIO_BUTTON (button));
>         button = gtk_radio_button_new_with_label(group, "button2");
>         gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (button), TRUE);
>         gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0);
>         gtk_widget_show (button);

>         button = gtk_radio_button_new_with_label(
>                      gtk_radio_button_group (GTK_RADIO_BUTTON (button)),
>                      "button3");
>         gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0);
>         gtk_widget_show (button);

>         separator = gtk_hseparator_new ();
>         gtk_box_pack_start (GTK_BOX (box1), separator, FALSE, TRUE, 0);
>         gtk_widget_show (separator);

>         box2 = gtk_vbox_new (FALSE, 10);
>         gtk_container_set_border_width (GTK_CONTAINER (box2), 10);
>         gtk_box_pack_start (GTK_BOX (box1), box2, FALSE, TRUE, 0);
>         gtk_widget_show (box2);

>         button = gtk_button_new_with_label ("close");
>         gtk_signal_connect_object (GTK_OBJECT (button), "clicked",
>                                    GTK_SIGNAL_FUNC(close_application),
>                                    GTK_OBJECT (window));
>         gtk_box_pack_start (GTK_BOX (box2), button, TRUE, TRUE, 0);
>         GTK_WIDGET_SET_FLAGS (button, GTK_CAN_DEFAULT);
>         gtk_widget_grab_default (button);
>         gtk_widget_show (button);
>         gtk_widget_show (window);

>         gtk_main();

>         return(0);
>     }
>     /* example-end */

> `

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